Field of the Invention
The present invention relates to an element substrate, which includes a heat-generating resistor element, and a method for discharging a liquid.
Description of the Related Art
Some liquid discharge recording apparatuses, such as an ink jet recording apparatus, employ an element substrate adapted to discharge a liquid by using a heat-generating resistor element. In this type of element substrate, a heat-generating resistor element may be subjected to a physical action, such as an impact caused by the cavitation in a liquid, or a chemical action caused by a liquid itself. For this reason, an element substrate is frequently provided with a protective layer for protecting the heat-generating resistor element from the foregoing actions.
Normally, the protective layer is deposited on the heat-generating resistor element, so that the protective layer is required to exhibit high heat resistance. Hence, the protective layer uses a metal, which has high heat resistance.
Further, in order to discharge a liquid by using a heat-generating resistor element, a voltage of a few volts to tens of volts needs to be applied to the heat-generating resistor element so as to bubble the liquid. In the case of the element substrate provided with the foregoing protective layer, a potential difference occurs between the protective layer and the liquid upon the application of the voltage to the heat-generating resistor element. If the potential difference exceeds a certain level, then the metal constituting the protective layer and the liquid may react with each other, causing the metal to be anodically oxidized or the metal to be dissolved into the liquid. As a solution, Japanese Patent Application Laid-Open No. 2001-080073 discloses a configuration in which an insulating layer is provided between a heat-generating resistor element and a protective layer.
In recent years, with increasing trend toward higher accuracy and higher speed in printing, liquid discharge apparatuses have been required to promptly discharge as much liquid as possible while minimizing the amount of liquid discharged at a time from each discharge port. Therefore, liquid discharge apparatuses have been developed to have a greater number of discharge ports and heat-generating resistor elements and to achieve a higher density thereof.
However, the heat generated by a heat-generating resistor element is transferred to a substrate, so that densely disposing many heat-generating resistor elements tends to cause the temperature of the substrate to rise. If the temperature of the substrate exceeds a certain level, then the discharge of the liquid may be adversely affected, which is typically represented by unstable bubbling of the liquid. If this happens, the printing must be interrupted until the temperature of the substrate decreases, resulting in printing slowdown.
Thus, it is required to transmit the heat generated by the heat-generating resistor elements to the liquid as efficiently as possible to suppress the temperature rise in the substrate. Making the insulating layer thinner allows the heat to be transmitted to the liquid more efficiently. However, making the insulating layer thinner may undesirably deteriorate the insulation properties thereof, resulting in a failure to obtain adequate insulation properties.
The present invention has been made with a view of the problem described above, and an object of the invention is to provide an element substrate capable of securing insulation properties while using a thinner insulating layer, and a liquid discharge head provided with the element substrate.